1. Field of the Invention
The present invention relates to a coating composition for a molded plastic article, and more particularly a coating composition for protecting the molded plastic article.
2. Related Background Art
Molded plastic articles are widely used, exploiting the advantages of light weight, ease of working, high impact strength, etc., but are associated with drawbacks of insufficient hardness and easy scratching, susceptibility to solvents, tendency of charging causing dust absorption and insufficient heat resistance. Molded plastic articles thus have been inferior to molded inorganic glass articles for the use in spectacle lenses and window panes.
For this reason it has been proposed to apply a protective coating to the molded plastic articles, and many coating compositions have been proposed for this purpose.
Such proposals include, for example, "a coating composition containing an organic silicon compound or a hydrolyzed product thereof as a principal component (resinous component or film forming component)" which is disclosed in the Japanese Patent Laid-Open Application No. 52-11261 and which has expected to provide a hard coating similar to an inorganic coating. This composition is commercially utilized for spectacle lenses.
However, since this composition is still unsatisfactory in scratch resistance, there has been proposed, for example, a composition additionally containing colloidal silica sol, as disclosed in the Japanese Patent Laid-Open Application No. 53-111336, and this composition is also commercially used for spectacle lenses.
However, such conventional coating compositions have been associated with a drawback of unsatisfactory performance of the coating film.